Polydopamine-coated CoS2@MoS2@CC for redox enhanced supercapacitors with improved electrochemical performances and suppression of self-discharge

Transition metal sulfides exhibit excellent energy density and specific capacitance in redox enhanced supercapacitors. However, the phenomenon of rapid self-discharge limits their large-scale development. In this study, we have analyzed an innovative and simple preparation of polydopamine (PDA) coated CoS 2 @MoS 2 @CC for redox enhanced supercapacitors applications. Considering the suppression the self-discharge of supercapacitors while also improving electrochemical performance of electrode. Subsequently, the densities of states, differential charges and adsorption energies of the PDA@CoS 2 @MoS 2 @CC and CoS 2 @MoS 2 @CC electrodes were calculated by using density functional theory (DFT) to investigate the mechanism of the effect of polydopamine on the performance of supercapacitors. PDA@CoS 2 @MoS 2 @CC electrode reveals a large specific capacitance (3520.45 mF cm −2 ) and outstanding cycling stability (92.75 % capacity maintenance after 10,000 cycles at 1 mA cm −2 ). This is because of the strong interaction between the PDA coating and K + , while K + are adsorbed in the PDA@CoS 2 @MoS 2 @CC electrode with high adsorption energy (-2.59 eV). It is convenient for the storage of K + . Therefore supercapacitors assembled with PDA@CoS 2 @MoS 2 @CC electrode also exhibit excellent performance (specific capacitance, energy density and power density are 511.85 mF cm −2 , 0.74 Wh cm −2 and 1.53 W cm −2 at 0.5 mA cm −2 ). It is important to investigate the self-discharge performance of the supercapacitor constructed by PDA@CoS 2 @MoS 2 @CC. Notably, the voltage of this device decreases to 0.73 V after 20000 s (initial potential is 1.7 V), which is better than the device assembled by CoS 2 @MoS 2 @CC (0.6 V after 20000 s). Further, the leakage current of this device is also less than the device assembled by CoS 2 @MoS 2 @CC at 1.7 V (0.05 mA vs 0.08 mA). This effective self-discharge suppression strategy is due to the free radical/singlet oxygen scavenging properties of PDA, which limits the parasitic Faraday reaction induced by diffusion-controlled, thus mitigating self-discharge.